An operon in E. coli called the Gua operon, encodes proteins responsible for guanine biosynthesis. Two genes, guaA and guaB are under the control of a single promoter and operator, similar to the arrangement in the lac and trp operons. A repressor protein, purR, binds to the operator. In what conditions (high guanine or low guanine) do you suppose this repressor binds to the operator? Do you consider this a "repressible" or "inducible" operon? 3 pts

Hight guanine"Repressible" operon

Explanation:

An operon is a fragment of DNI with genes that encode for different proteins of metabolic vias. Operons are composed of a regulator gene (that codifies for the repressor), the operator region (that links with the repressor protein), and the promotor sequence (RNA polymerase recognizes the promotor where it begins the RNA synthesis).

The repressor deactivates the expression of a gene when binding the operator of that gene. This binding does not allow the production of mRNA, and hence, proteins that this molecule should synthesize.

This protein has a negative effect on genic expression impeding the transcription of RNA from DNA.

Operons might be inducible or repressible. When the operon is inactive, and a little inductor protein activates it, then the operon is inducible. On the contrary, the repressible operon is the one that is normally active, but the little corepressor protein inactivates it.

During high guanine concentration, the repressor protein must act to regulate the amount of guanine in the environment. Hence it links the operator of genes guaA and guaB to stop the biosynthesis. The operon was initially active, but then by the union of the repressor, it gets inactivated. This is a "repressible" operon.

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